Hubris or Over Confidence
From dictionary.reference.com Overbearing pride or presumption; arrogance: "There is no safety in unlimited technological hubris" (McGeorge Bundy).
What happens is: ;a biker takes some training or takes some other measure to improve his or her safety, develops an over-confidence and goes out and crashes.
Just because you did something to improve your safety doesn't make riding a safe activity, and that sense of false security can kill.
The phenomonen is so widespread there's even a name for it, Risk Homeostasis. Humans have an inbuilt tendency to negate the benefits of risk reduction in one area by indulging in riskier behavior in another area.
Many of the things on this site can help with bike safety, but even in the unlikely event that someone could do them all, biking would still be a very risky activity. Taking an individual step to improve safety is a good thing, but adjusting our mindsets is the ultimate objective.